Radio system for providing vertically separated airways



Dec. I9, 1950 M. W RADIO SYSTEM FOR PROVIDING VERTICALLY ALLACESEPARATED AIRWAYS Original Filed Sept. 21, 1940 8 Sheets-$heet lJPOM/ff? ETE-m.. E'

INVENTOR.

F4 M41" BY Dec. 19, 1950 M. WALLACE 2,534,840

. RADIO SYSTEM FOR PROVIDING VERTICALLY SEPARATED AIRWAYS Original FiledSept. 2l, 1940 8 Sheets-Sheet 2 :Fic-f... E A

I'ANSM/ 775,4? PLA rE Fc FM SAWTOOTH OSG/LA TOR g Dec. 19, 1950 M.WALLACE RADIO SYSTEM FOR PROVIDING VERIIOALLY SEPARATED AIRWAYS 8Sheets-Shearl 3 Original Filed Sept. 2l, 1940 Dec. 19, 195o M WALLACE2,534,840

RADIO SYSTEM F'OR PROVIDING VERTICALLY SEPARATED AIRWAYS Original FiledSept. 21, 1940 8 Sheets-Sheet 4 I V* WW- un -w C my' J z s In U A@ r l"i I l l C l'l' N N T w V Il AH o f l( v j w 5 hmm @3l D 19 1950 WALLACEec RADIO sYsImNIIoR PROVIDING vER'rIcALLY SEPARATE!) AIRwAYs 8Sheets-Sheet 5 Original Filed Sept. 21, 1940 hllllll lrll l lll llll YINVENTOR. QlZva/oce/ 2f/@H70 cv,

Dec. 19, 1950 M. WALLACE 2,534,340

RADIO SYSTEM FOR PROVIDING VERTICALLY SEPARATED AIRWAYS 4Original FiledSept. 21, 1940 8 Sheets-Sheet 6 Dec. 19, 1950 M. WALLACE 2,534,840

RADIO SYSTEM FOR PROVIDING VERTICALLY v SEPARATED AIRWAYS Original FiledSept. 21, 1940 8 Sheets-Sheet 7 Dec. 19, 1950 M. wAkLAcE 2,534,340

RADIO SYSTEM FOR PR VIDING VERTICALLY SEPARATED AIRWAYS Original FiledSpt'. 2l, 1940 8 Sheets-Sheet 8 INVENTOR. 976cm :ce L 9x/41511160,

APatented Dec. 19, 1950 RADI SYSTEM FOR PRQVIDING VERTI- CALLZ SEEARATEDARVJAYS lriarcel Wallace, New York, N. Y., assignor, by mesneassignments, of one-half to Panoramic Radio Corporation, New York, N.Y., a corporation vof New York @riginal application September 21, 1940,Serial No, 357,814, now Patent No. 2,378,604, dated June 19, 1945.Divided and this application April 14, .1945, `Serial No. 588,396

Z Claims.

My invention relates broadly to systems of radio navigation and moreparticularly to improved methods and circuit arrangements for radiobeacons and panoramic reception for use in navigation of mobile bodies.

'This application is a division of my Patent No. 2,378,604, issued June19, 1945, for Radio Altimeter and Panoramic Reception System.

In my Patents No. 2,279,151, granted April 7, 1942, for Panoramic RadioReceiving System, and No. 2,273,914, granted February 24, 1942, forRadio Navigation System, I have shown that by means of a frequencyscanning panoramic receiver installed on board an airplane, it ispossible to observe `one or a plurality of signals which are radiatedfrom transmitting stations located at danger points, such as mountainpeaks. ior warning the pilot of the approach of the plane to terrainwhich may be hazardous to aerial navigation.

One of the objects of my invention is to provide a system for emitting asignal of such a nature as to inform those who receive it, oi' thealtitude of a fixed or mobile body equipped with the apparatus of myinvention.

A further object of my invention is to provide an arrangement of asignal generator which can be synchronized with a receiver on board amobile body, in such a manner that the .signal supplied .by thegenerator does not interfere with the reception of another signal at thesame frequency originating from another body.

Another object of my invention is to provide sim-ple apparatus for thereception and convenient interpretation of a plurality oi` signalindications, and information which can be received visually, or bothvisually and aurally.

A further object of my invention is to provide simple transmitting andreceiving apparatus for providing navigational information withoutmoving parts and with all the circuits electronically controlled.

A still further object of my linvention .is to `provide a simple systemfor distinguishing between signals of a given system and others ofanother system although such beacons may use the .same portion of thefrequency spectrum, 4by changing the rate of :frequency change from `onevsystem to the other. This is rendered possible by the use of frequencyscanning panoramic receivers `having means for varying at will theirrate of frequency sweep, so as to make it correspond to the rate `offrequency variation, or of a harmonic thereof, of a signal. This featurepermits the elimination of sources of periodic noises such as producedby vibrators, motors, etc.

Another object of my invention is to provide means for traffic controlat airports, ,and therefore permit handling of large numbers .0faircraft during conditions of poor visibility.

Still another object of my invention is to provide an absolute altimetercontrol requiring no adjustments, along airways and airports.

Another object of my invention is to combine such altitude indicationsand traic controlling system, with means for communication to selectedstations.

Still Aanother object of my invention is to provide means for signallingfrom the ground to particular aircraft selected according to theiraltitude.

Still another object of my invention is to permit aircraft to fly in.dilerent directions along such airways .and maintain a certain minimumand maximum vertical separation between them.

Another object of my invention is vto simplify methods of instrumentlanding by using the absolute altitude as indicated from the airport, asa vertical indication and to combine such indications 'with those ofdistance and direction.

Another object of my invention is to provide means for aircraftidentification either from air. craft to aircraft or from ground toaircraft.

Other and further objects of my invention will be apparent from thespecifications hereinafter 1a is a block diagram showing therelationships between an aneroid cell, a transmitter and ,a re

ceiver according to my invention; Fig. 2 .is auf other block .diagramshowing ,in a more detailed for-m the principal parts and theirrelationship in a fully electronically controlled irequency scanningpanoramic receiver, and of an aneroid cell controlled transmitter, saidreceiver .'aul'f@ matically keying off the transmitter .so .as toprevent interference between the two; B represents a .series ,of curvesshowing the frequency versus gain and power relationships between thevarious elements shown Figs. 2 and 4.; Fig. :3a represents a series ofcurves showing -the phase relationship between the :sawtooth voltagecontrolling the periodic response of an aural device and the periodickeying Aof a transmitter as :shown in Fig. 4a; Fig. 4 is a detaileddiagram cf ia receiver `such as representedin Fig. 2.; Fig. dais a.similar receiver combining electronic and mechanical means; .5 is ablock diagram .of another electronically controlled receiver andtransmitter similar in function to those shown in Fig. 2, with thedifference that the said receiver is simultaneously indicating signalspresent over distinct portionsv of the frequency spectrum; Fig. 6 showsdetails of the special elements used in connection with the apparatusshown in Fig. Fig. 7 shows a series of curves explaining the time andvoltage relationship of various elements of Fig. 5; Fig. 8 is a specialdynamically balanced condenser combined with a synchronous commutator;Fig. 9 is a diagram of an apparatus in which the device of Fig. `8 isused; Fig. l0 shows a commutator and its connections for obtaining asquare wave current; Fig. 1l is a schematic diagram showing amechanically controlled frequency scanning panoramic receiversimultaneously indicating two bands of the frequency spectrum and usingthe devices shown on Figs. 8 and 10; Fig. 12 is a diagram explaining thephase relationship between elements of Fig. 11; Fig. 13 is a schematicdiagram representing part of a panoramic receiver using an electronicsource of sweep voltage, a mechanical commutator and a periodicallytunable condenser. It also shows the method of synchronizing theseelements; Fig. 14 represents a block diagram of the principles used in adual-frequency beacon according to my invention, in which twotransmitters are continuously operated; Fig. 15 represents a screen ofan aircraft type receiver embodying the features of my invention; Fig.16 Yrepresents the screen of a similar ground type receiver; Fig. 17represents the phase relationship between a sine wave used for cathoderay sweep and transmitter modulation, and a pyramid wave for frequencysweep; Fig. 18 shows a vertically defined airway, with verticalseparation for aircraft traveling in opposite directions; Fig. 19 is ablock diagram of a simplified transmitter in which twooscillator-transmitters are alternately operated; Fig. 20 shows a seriesof vertical level markers leading planes to a landing runway from avertically defined airway; Fig. 21 shows the appearance Aof the screenand dial arrangement of a dual band frequency scanning panoramicreceiver, showing simultaneously a plurality of beacons, theirrgeographicV position and also a plurality of obstacles and theirrespective altitudes withv respect to the observer; Fig. 22 is areversible transmission pattern of a dual-frequency beacon creating anequi-signal path; Figures 22a and 22h show how certain signalstransmitted from a transmission pattern such as shown in Figure 22appear on a frequency scanning panoramic receiver; and Figure 23 is adiagram of a wind controlled directive beacon. In the carrying out of myinvention, advantage is taken of the properties of a frequency scanningpanoramic receiver, such as described in my patents, supra.

' In the system of my invention, I provide means capable of:

' l. Continuously observing the variations of signal strength of two ormore signals.

Y2. VObserving the variations of frequency of two or more signals.

3. Determining the frequency of modulation of any signal, bysynchronizing the band sweep frequency with the modulation lof thetransmitter.

' Considering the large number of special terms required in connectionwith the technique of frequency scanning panoramic reception, and inorderA to avoid repetition of explanation, or misinterpretation of theseterms, I shall referfin the it at the point of origin.

l frequency spectrum.

d; description which follows to standardized terms whose definitions aregiven herein below:

A panoramic receiver is a radio receiver having means for reproducing ona cathode ray screen substantially simultaneously in the form ofindividual signs, the frequency and amplitude characteristics of aplurality of independent signals distributed over a given portion of theradio When the presentation is produced by frequency scanning, orperiodic tuning of the radio receiver, the receiver is known as afrequency scanning -panoramic receiver.

By signal strength (s) is meant the input strength of a signal measuredin microvolts at the antenna terminals.

The frequency sweep axis is the line traced on the screen of the cathoderay tube. Its point of origin corresponds to the point on that linewhere the luminous spotstops, when the sweep voltage applied to thedeilecting elements passes through Zero value. Y

The amplitude axis is the imaginary line normal to the frequency sweepaxis and meeting Frequency sweep rate is the number of tim the frequencyscanning panoramic receiver is periodically tuned during an interval ofone second.

The deflection amplitude (o) is the linear deflection produced by asignal, measured on the amplitude axis.

Amplitude discrimination, for a given gain control setting, is the ratiodv/a's between the increase of deflection amplitude (du) and theincrease of signal strength producing it (ds). It is a linear amplitudediscrimination when the amplitude discrimination remains constant forany value of signal strength auf) ds s It is a non-linear amplitudediscrimination when the amplitudeY discrimination varies with variationsof signal strength,

The logarithmic amplitude discrimination is a non-linear amplitudediscrimination in which f(s) is a logarithmic function.

The visual frequency range is represented by the minimum frequency Fmand maximum frequency FM corresponding to the extremities of thefrequency sweep axis.

The frequency sweep is the difference between FM and Fm and representsthe bandwidth visually covered.

The frequency spacing is the band width representing in kilocycles,covered over one linear unit along the frequency sweep axis. It isexpressed, for example, in kilocycles per mm.

The origin frequency is the frequency at which the receiver is tuned atthe point of origin on the frequency sweep axis.

The center frequency is that frequency which is substantially equallyseparated from FM and Fm and is, therefore, in the center of the visualfrequency range.

Tuning a panoramic receiver, is the action of displacing the origin orcenter frequency along the frequency spectrum.

Tuning range is represented by the minimum and maximum frequenciesreceivable (in kilocycles) by tuning the panoramic receiver from one endof a band tothe other, (Fmin and Fmx).

ausgew f.

s, "Frequency range is the number of kilocycles resulting from thedifference between Fmax and Firm.

Bias tuning is the panoramic tuning obtained through the variation ofbiasing voltage on the reactor tube.

In order to explain the operation of my invention I must first refer tosome well known principles involving the generation of a signal whosefrequency is characteristic of the altitude or of the local pressure. Aportion of the frequency spectrum may be assigned for the purpose ofthese indications, and may be subdivided according to a predetemnnedrelationship between frequency and altitude. 'I'his relationship Vmay belinear. For example, if for altitude zero, (corresponding to sea level)the frequency Fmin is assigned and for an altitude of H feet, afrequency Fmax is allotted, any intermediary altitude, for example h,can conveniently correspond to a frequency This. term will be called inthe future: the altitude frequency corresponding to altitude h.

Instead of this simple linear frequency versus altitude distribution,other functions may be determined. which instead of being linear, canbe, for example, exponential, the frequency varying proportionally tothe percentage of altitude variation, etc. An element such as analtitude or pressure operated instrument is employed for controlling thefrequency determining circuit of the signal generator.

Such a generator is shown in Fig. l, in which an aneroid cell I.,supported by block ll,` is made to vary the dist-ance between condenserplates 2 'and 3. The capacity of the condenser 2-3 varies according tothe local pressure as impressed the aneroid cell. This condenseroperates to tune a circuit. including an inductance 5 and the wholetuned circuit determines the frequency of oscillation of a tube 6. Thisis a simple type of local pressure of altitude indicating oscillator,

which is employed in several arrangements of invention describedhereinafter.

The readings of the frequency indications of several such oscillators,may be made with a panoramic receiver, or by a frequency scanning'panoramic receiver, such as described in my patents, supra. Thefrequency sweep axis on the cathode ray tube can be calibrated inaltitude, and from the position` of each deection, the altitude of eachobstacle can be read.

When such an altitude indicating signal. generator is. mounted on boardaircraft and if this aircraft carries on board a panoramic receiverwhich tunes in the altitude band of the frequency spectrum, the locallygenerated signal covers that part of the spectrum which corresponds toits own altitude frequency. If another aircraft equipped with anidentical altitude indicating signal generator is inthe proximity of thefirst, and at. the same altitude, the observer may not beableptherefore, to. distinguish its signal, on account of said localsignal which interferes with the other signal presumably weaker.

My present. invention removes this difficulty. In. order tor do this, Iprovide a combination between the local signal generator and thepanoramic receiver, in such a manner that the out'- lmflpower of thefirst is controlled in synchronismthe periodic tuning of the other. Bymeans of a synchronous switch, which can be either elec- 6 tronic (Figs.2, 3, 4) or mechanical (Figs. 3a, 4a), the transmitter is shut oirentirely, or only reduced in power, periodically, every time thereceiver tunes through, or must indicate a frequency close to that ofthe local transmitter.

Such a combination is represented as a block diagram in Fig. la.

Icall such a combination between a panoramic receiver' and an aneroidcell controlled transmitter, which operate in synchronism with one-another a Stratoscope, a word which will be used from time to time todefine this instrument.

An electronically controlled stratoscope is shown in Fig. 2 in the formof a block diagram for explaining my invention. The frequency scanningpanoramic receiver illustrated consists of a signal input circuit A, anoscillator B, a converter C and two channels of intermediate frequencyamplifiers D and E. The oscillator is periodically tuned over a band offrequencies by a Variable reactance tube F which, in turn, is controlledby a sweep voltage generator G. 'Ilhis generator produces the source ofsweep voltage applied to one set of deflecting plates of the cathode raytube H. The intermediate frequency channel D is sharply tuned and thesignals passing through it are detected and applied to the other set ofdeilecting plates of the cathode ray tube.

The parallel channel E is broadly tuned or tuned slightly on thefrequency of channel D and develops at its peak a much weaker signalthan channel D. However, over certain portions of the frequencyspectrum, immediately adjacent to the `band pass characteristics of thechannel D, it develops a stronger signal.

This is illustrated in Fig. 3, in which the Iabscissa represents thefrequency variation (or time variation, the two being linked together)and the ordinate represents gain of channels D and E or power developedby oscillator transmitter J.

supposing that the oscillator transmitter J emits a signal on frequencyFh and the frequency scanning panoramic receiver starts tuning from afrequency Fmin toward a frequency Fines. As it approaches frequency Fhit passes through a region F1F2 when the I. F. channel E develops animpulse which is applied at once to a keying tube which triggers off thetransmitter J (see curve J on Fig. 3), before or almost at the time-when the channel D could start building up a signal from thetransmitter. The time constants of the trigger circuit are such as tomaintain the transmitter keyed off during the predetermined timeinterval, equivalent to a variation of frequency of from F3 to F4. Whenthe oscillator starts again, its frequency is out of the tuning range ofthe receiver, so that the latter is unaffected by the presence of thatlocal signal. The signals picked up by the channel D are detected,amplied and applied to the other set of deflectlng plates of the cathoderay tube H. These signals will be always synchronized with the sweepVtrated in Fig. 4a, as S''a and 34h. This is iin#-v portant in case ofcollision warnings. The speedV of 'the planes being great, it ispossible that the pilot may not be aware of the appearance of a visualdanger signal on the screen, but his attention would be drawn at once ifthis signal will produce a distinctive noise in the loud-speaker or alight on the panel, which is exactly what happens. This is a veryimportant feature of my invention, which adds to the safety of theflier.

In the circuit diagram of Fig. 4, the input circuit A is constituted bya receiving antenna 8, an inductance tuned by condenser 9 and anamplifier tube I2. The frequency modulated oscillator B is constitutedby the triode I4 and a circuit tuned by condenser l I. Directlyconnected to the tuned circuit of this oscillator, I show the frequencymodulating channel F constituted by a thermionic tube I which acts as areactance in parallel with said tuned circuit. By properly adjusting thephase relationship between the input and output circuits of tube I5, asdetermined by capacities, resistors and choke (G, lll, d2) the rcactanceof this tube will increase or decrease the frequency of the oscillatorI4 by an amount depending on the voltage impressed on the grid 0.3 ofthe tube l5 in a direction depending on its polarity.

An alternating voltage, preferably produced by a sawtooth oscillator I6and amplified by tube I1 (corresponding to G in the block diagram) isfed to the variable reactance tube I5, through a potentiometer 26 and avoltage balancing potentiometer 1l! which is shunted by a battery 1 I.The adjustment of potentiometer 1Q controls the biasing voltage on thegrid 43, consequently the average reactance value of the tube I5. Itdetermines, therefore, the average frequency at which the receiver willoperate when an alternating voltage is fed on the grid 33. Thepotentiometer 25 controls the amplitude of this voltage, which in turncontrols the reactance variation of tube I5, and, therefore, thebandwidth of oscillator i4. The frequency of the sweep voltage can beadjusted by means of a multi-position selector switch 28 and the platevoltage controlling rheostat 31. This frequency can be tied up orsynchronized to any desired periodic voltage source, such as powersupply, etc.

The converter corresponding to C is tube I3 whose grid is coupled to theinput amplifier tube I2 and frequency modulated oscillator I4. Theconverted signal is developed in the I. F. transformer 5 having twosecondaries shown at 36 and 5T. The secondary 35 is tuned to the samefrequency as the primary of transformer 45 and feeds the high gain,sharply tuned channelV corresponding to D, composed of two amplifyingstages comprising the tubes I8 and I9 andtransformers 4B and 41.

The signals are then detected and reamplified by means of a combineddiode-triode thermionic tube 2Q. One diode plate 8 applies the rectifiedsignal to a resistor 54 and the voltage drop through it is used toautomatically control the gain of the amplifying tubes IB and I9 byapplying appropriate voltages at their grids through resistors 50 and 5I, which are by-passed with condensers 52 and 53. The action of thisautomatic volume control is very important in the operation of thesystem of my invention, because it will prevent a signal from buildingup in amplitude beyond a given point, and instead, will compress theother signals weaker than it, so as to maintain their amplitudes asindications of their eld strength. It will also tend to equalize rapidF. stages.

variations' of deflection amplitudes due to varia-y of signal strengthcaused by reflections.

The time constant of the circuits must be longer than the time period inwhich the receiver is tuned from minimum to maximum so thata signalimpulse received in one tuning cycle will exert its volume controlaction in the `next tuning cycle or cycles.

strengths by the difference between their corresponding deflections. Y

The other diode plate 49 is connected to the diode 48 by means of acondenser 55 and de-A.

velops a rectified pulsating current which is applied to an amplitudecontrolling potentiometer 30 and from there through a condenser Vii'tothe grid of the triode section of the tube, which acts as a lowfrequency amplier of the pulsating current. Y

A potentiometer SI is provided for the important function of"thresholding the signals. This operates as follows: The diode plate 49of the diode-triode tube 20 is returned to the power supply circuit bymeans of resistors 12 and 13'; to this potentiometer 3l a leg of whichis at ground potential. The anode potential is taken from the cathoderay elements power supply 14" which is dropped to ground potentialthrougha series of resistors including 15, 16, 11 and 18,'

some of which act as focus and intensity controls for said cathode raytube.

By being able to make the diode plate i9 of any potential desired fromzero up to a few hundred volts negative, it is possible to out out orprevent detection of any signal which does not exceed a desired value.

is useful for eliminating either noises which are below the signallevels or weak signals which arev not interesting to the observer andwhich may'k confuse him. This threshold potentiometer' canbe calibratedin field strength, whether micro-` volts or decibels for measuring thefield strength of any signal. It is therefore useful also for measuringthe difference between deflection amplitudes, which as said above,corresponds to ratio between signal strengths. i

The potentiometer 30 which controls the amplitude of the signals appliedto the output device, will cut all deflections in such a manner as toreduce them all in the same proportion. Therefore, the deflection ratiosremain constant. By

using, however, the threshold control we change the ratio between thedeection amplitudes and this becomes useful when we want to exaggerateor emphasize the difference of two deflections nearly equal inamplituda-as is necessary in the dual-frequency beacons describedhereinafter.

The pulses resulting from the reception'of a series of stations are ofextremely short duration, this depending upon the frequency of thesweepvoltage, the band-width and selectivity of the I. This means thatthe amplifier must have certain frequency characteristics which permitthe amplification of frequencies of the order of ay few thousand cyclesper second.` These frequency characteristics are determined bythe valuesof the grid, plate and cathode resistors A resistor 59 connected to thehigh Its action may be amplified if desired and this action actuallydetermines the This control acts, consequently, as an adjustablethreshold device, whichv under conditions of varying load. The amplifiedpulses are appliedthrough a condenser 6I to one deilecting plate 62 ofthe cathode ray tube 23, but it can also be connected by means of aswitch 35 to an auditive output stage or device 3d for the audible oradditional visual warning. The perpendicular deflecting plate 63 of thecathode ray tube is connected to the sweep voltage generator I6 afteramplifying its output through tube II. The frequency of this sweepshould be sufficiently high to produce a rapid sweep of the cathode raybeam, which should appear substantially ilickerless on the fluorescentscreen of the cathode ray tube.

The secondary 31 of I. F. transformer 45 feeds the transformer 64 whichiss/,connected to a diode detector and amplifier tube 2| whichcorresponds to the amplifying channel E of Fig. 2. A very strong signalproduces across the condenser 65 andresistor 66 a substantial negativevoltage which is applied to the grid 68 of a keying or trigger tube 22(corresponding to I). The plate of this tube is connected to the cathodeof the transmitter oscillator tube 6 whose frequency is controlled, asexplained hereinbefore, by the variations of pressure as impressed uponaneroid cell I.

The tube 22 oifers the proper amount of resistance in the cathode leadof the oscillator 6 when no signal is applied to the grid 68, which isreturned to ground by the grid resistor 61.

The signal, however, builds upon the condenser 69 and grid 68 a negativevoltage which triggers off the plate current of tube 6 which stays shuto until the charge of condenser 69 leaks out through resistors 66 and61.

The time constants of this circuit can be adjusted to keep thetransmitter turned off just the length of time desired, as explainedhereinafter.

The voltage developed by the tube 2I is low even when signalsoriginating at a certain distance are present, but is great in thepresence of the local signal, which builds up to several hundredthousand micro-volts in that stage,

before the sharply tuned stages I8, I9 have time A variable coupling actas a filter of broad band pass characteristics.

All the potentials required for the frequency scanning panoramicreceiver are produced by a common source of power supply and all canhave a common ground return to the chassis.

The frequency scanning panoramic receiver described herein can be madeto cover a rather substantial band by ganging the condensers I0, II, orby using band filters. The bandwidth of the receiver will be determinedby the voltage variations applied to the grid 43 of tube I5, which iscontrolled by the potentiometer 2a. The latter acts, therefore, as aband expansion or band compression device. If the constants of thecircuit of tube I are properly adjusted, it is possible to make thefrequency shift of the oscillator I4 substantially equal both above andbelow its average frequency, which permits a panoramic observation ofequal bands immediately above or below a given center frequency. If thetotal band width is not too great, the input stages I2, I3, may be madeof suciently broad band pass characteristics to avoid the necessity oftuning the condensers 9 and I0 and still obtain substantial linearity ofresponse over 10 the desired band, as illustrated in Fig. 4a. Thecondensers 9 and I0 are substituted therein by condensers 9a, 9b andIlla, I 0b, which are permanently adjusted to admit a band of therequired Width.

It is possible to tune, or vary the center frequency of the frequencyscanning panoramic receiver by either adjusting the oscillator condenserII or by adjusting'the center arm of 'biasing potentiometer 1B. Thisvariation can take place either manually or automatically and in thelatter case it can be effected by either the saine aneroid cell I, whichcontrols the transmitter-oscillator, by mechanically linking it tocondenser I I or by another similarly constructed aneroid cell, as shownin Figs. 4a, 11a and l5. 1n Figs. 4 and 4a, I have shown a dotted linebetween lcondensers II and 3 and aneroid cells I, Ia, and Ib to show amechanical link.

This control of the condenser II by an aneroid cell will aifcrd aconstant retuning of the center frequency of the panoramic receiver,this representing at all times the local altitude frequency. Thefrequencies above and below is represent altitudes above and below itand the bandwidth can be such as to cover an altitude of, for example, nfeet above and n feet below the airplane. The scale can be expanded orcontracted at will. This is useful if the frequency assignment covers arelatively Wide band, so as to take care of very' great altitudes. Theceiling of modern planes increases continuously and if we would have tocover on a few inches of an oscillograph screen at all times the entireband, the readings may be difficult to make or would not have sufficientaccuracy. y

With this method of centering the observation and limiting it by bandconstruction to certain vertical levels above and below Vthe observer,this objection is removed and, besides, the pilot has all the warningand information he wishes, as he is not interested in what happens toohigh above or too far below him.

The centering of the local altitude, corresponding to the localaltitude-frequency greatly slmplifles the design of the commutatorcontrolling this signal. This commutator can be also `rnechanical asshown in Fig. 4a, acting every time when the receiver tunes through thecenter region of its band.

In this ligure, |05 represents a rotating shaft, which can be that ofthe motor-generator I'B producing the plate current supply, and which isat ground potential. The plate current of the transmitter from thecathode of the oscillator tube S passes through a brush 20I which rideson a metal ring 20M grounded through the shaft E05. A narrow segment200e, of an insulation material periodically interrupts this current,therefore keying olf the oscillator tube 6. On the same shaft |05 aninsulated ring IIJUd, having a narrow grounded segment IEIc, and a brushIUI, form the elements controlling the charge and discharge of acondenser I04 through a resistor |03. A source of sawtooth voltage iscreated Vand this is amplified through tube I'I and. used forcontrolling both the movement of the cathode ray on the screen(deflecting element 63) and also to periodically vary the reactance oftube i5, and accordingly the frequency of the receiver oscillator I 4,through a. three position bandwidth control 25a, b. The phaserelationship betweenvthe sawtooth voltage and the keying of theoscillator is determined, once and for all, by the relationship of theat his own level.

l of aural as well as visual signaling for navigavmarker beacons.

Abrushes l! and 20|, and of the segments I00c and 200e.

` Fig. 3a shows such a time relationship. The upper line represents thesawtooth voltage curve which, in this case, includes a small time periodi t1). representing the current at ground potential as determined by thewidth of the segment 100C. This time period can, however, be reduced to.negligible value by making that segment very thin. The second linerepresents the variation ,of plate current in the transmitter showingthe 4time periods when this is oif (t2) this total time period dependingupon the width of segment -200d. The sharper the circuits of thereceiver,

the narrower can be made this segment. By spacing the segments |000 and200d, 180 apart, and by maintaining the brushes |01 and 20| in 'the sameplane, the interruptions tz will take .place at the moment when thesawtooth current passes through its center value, and therefore when thereceiver tunes through its center frequency, or in other words, when thestratoscope screen indicates its altitude frequency.

Whereas in Fig. 4, I have shown one aneroid .cell I driving the twocondensers 3 and Il, 1n .Fig 4a, I show two separate, but identicallyop- .erating cells, la and Ib, each driving one condenser. In the latterfigure I also show bandpass input circuits requiring a singleadjustment, and

va selective audio response circuit described be- ..low.

Frequency selection- By connecting headphones or a loudspeaker in theoutput of the detector, a'sound will be heard when a signal appears onany portion of the tuning range. This will, as said before, act as analarm for the pilot.

' the detector is fed through a push-pull amplifyingrstage 202er, 2021),and a selecting commutator 35a, 315C, 35d, to headphones 34a and/or aneon bulb 34h. This stage 202a, 202D, operates only periodically whenthe brush 35a connected to the cathodes of tubes 202e and 202D isgrounded through the metal segment 35e of the rotary commutator 35d.This commutator is rotated together and in synchronism with the othercommutators on shaft |05. By adjusting the vposition of the brush 35aaround this shaft, by

. means of a dial, we can select any portion of the .bandwidth where theheadphones will respond, f in other words, any frequency within therange of the receiver. If a signal is present at that frequency achopped noise is heard. I use a properly balanced amplifying stage, inorder to eliminate the commutation click so that only the actual signalscoming through the detector are heard. By setting the brush 35a in agiven fixed position, for example corresponding to the center frequencyof the receiver, only signals corresponding to that frequency can beheard. This position may be used permanently and is important for threereasons: l. Because the pilot will receive definite indication of actualdanger from an obstacle (plane, for example), situated 2. Because itpermits means tional and traffic control, as it will be shown below. 3.Because it permits special uses of ground Such a condition isrepresented in Fig. 3a in which I show on the lower line the vphaserelationship between the response of devices 34a, 34h and the sawtoothvoltage (which is linked to frequency variation) .The solid lines showthe last condition described, that is a respense at the centerfrequency. The dotted lines on the left of the rst, represent responseat a frequency nearer to Fm. l

It is possible to link the frequency of one os'- cillator to the otherby many other means, some being electronic, wherein a variation offrequency can be converted, for example, in a variation of voltage andthen apply this variation of voltage to the other oscillator to create avariation of frequency again. My receiver is ideally suited for suchtypes of control because I can convert variations of voltage easily intovariation of frequenciesfthrough the changing of the bias volt age l! onthe reactor tube l5.

In my above mentioned patents, supra, I have shown how I cansimultaneously receive on a frequency scanning panoramic receiver twobands of frequencies which can be observed on two different portions ofthe oscillograph tube. Thisis a very important requirement if thereceiver is to be used for navigational purposes, so as to avoidcarrying onboard several receivers. It may be assumed, for example, thatthe flier wishes to follow a string of radio range beacons and alsoavoid any dangerous obstacle, xed or'mO- bile. 'Ihe string of beaconsmay operate on one continuous band of frequencies different from thealtitude frequency band. An electronically controlled receiver showingsimultaneously two bands of frequencies can be used advantageously forthe purpose. Such results can be obtained in the following manner:Synchronously with the sawtooth generator, I provide means forgenerating a square-wave alternating current. This is composed of aseries of electrical impulses of a constant amplitude, each such impulsehaving a duration equal to the duration of one sawtooth cycle. Theseimpulses are intermittent, each being followed by an equal time periodwhen no current is generated.

Fig. 7 shows on its lower part at M three such square-wave pulsatingcurrent impulses; N represents six cycles of synchronous sawtoothcurrent impulses and M-l-N represents current resulting from thecombination or addition of these two types of impulses. The frequencycontrolling tube I5 (F in the block diagram, Fig. 5), in which I providea circuit for feeding a current such as the one represented as M-i-Nwill alternately cover two bands of frequency whose separation from eachother will be determined by the amplitude of the square-wave input. y

At the top of Fig. '7 I show an ordinate representing frequencyvariation as produced by such a combination wave in the variablefrequency oscillator. It alternately covers the frequencies F1, F2 andF3, F4. The frequency separation between F2 and F3 can be reduced tozero by'reducing the amplitude of the square-wave voltage or beincreased to a maximum by increasing that voltage. It can., therefore,be seen that variations of amplitude of M will shift only one band offrequencies (F3 to F4) and will not affect the other band. This shiftcan be obtained in the simplest manner by applying the square-wavedirectly-to the biasing potentiometer or resistance 10 (Figs. 4 and 4a).i

Fig. 5 represents another block diagram showing how this receiveroperates. The same letters are used as in Fig. 2 for the common elementsof the two types of receiver transmitter combinations. In Fig. 5 inaddition S represents i3 the square-Wave generator, and T the mixerofthe sawtooth and square-wave currents. Previously to being mixed, thesawtooth component is applied to one of the deflecting plates 53 of thecathode ray tube and the square-wave component to another deflectingplate 62, normal to the first, where it is combined with the signal fromthe channel D.

The elect of this application of the square- Wave is to recurrently, andat the end of each cycle of the sawtooth wave, shift the frequency sweepaxis of the cathode ray tube, so as to alternately obtain two parallellines on which the 'signals contained in the bands F1 to F2 and,

respectively, F3 to F4 will appear.

The linear separation between these two parallel frequency sweep axes isa function of the amplitude of the square-wave voltage applied to thedeflecting plate 62, and this is controlled Ithrough any appropriatemeans.

Fig. 6 shows a detailed diagram of the elements G, Sand T of Fig. 5.Tube 80 is a double triode,

the grids of which are cross-connected in such a way that each triodesection becomes alternately blocked. The frequency of this blockingfaction is determined by the rate of charge and necting the grid 89 oftube 8| to one of the plates of the tube 80. The frequency control ofboth tubes is, therefore, obtained by single controls 88a, 88h, 88e and81a, 81h and 81e.

Tube 82 is another double triode which is used in the event that highsignal voltages are required. Tube 82 acts as an amplifier in connectionwith the sawtooth and square-wave oscillators.

The amplitude controls 92 and 93 are used to control the voltage of thedeiiecting currents put into the vertical and horizontal deflectingplates respectively, of the cathode ray tube and the amplitude controls94 and $5 are used to control the voltages applied to the grids of themixing tube 55 (T in Fig. 5). The mixed current obtained from the platesof this tube is applied to the frequency controlling tube F.

The same results, as obtained by purely electronic means of tuning, canvery well be obtained by either purely mechanical or combined electronicand mechanical means such as illustrated in Figs. 8, 9, 11 and 13. Themechanically fre-V quency modulated oscillator is quite practical andreadily made. A rapidly rotating motor driven condenser produces thefrequency shift required. One precaution, however, must be taken inavoiding `frictional contacts in the tuned circuit, which are invariablynoisy, mostly at high frequencies. The best method to avoid this is byusing insulated or floating rotors, varying the capacity between twoopposite stators. Another precaution which must be taken is to properlybalance the rotors dynamically, so as to avoid vibration. This can beobtained by using rotors having several blades, two, three, or more.Such a twobladed rotor is shown at Sta, 95h, in Fig. 8.

The effect of such multi-bladed rotors is to speed up the number ofimages for a given motor speed. In ultra-high frequency work, Where theperiodical variation of capacity required is quite small and amountingonly to a few micro-microfarads, I prefer to obtain the capacityvariations necessary by simply rotating a rotor of high dielectricconstant between two stator plates connected in the tuned circuit.Several such dielectric rotors can be coupled on one shaft to tune asmany circuits as required. One of these rotors can be used formechanically producing a source of sweep voltage, by the periodicalcharge and discharge of a condenser, as described in Fig. 4 and in mypatents, supra. Fig. 8 is an example of such a construction, in which96a, 96h represent the two blades of a dielectric rotor having a openingand rotating between one or two pairs of stator blades 97a, 91h and 98a,98h. We have in fact two distinct variable condensers which can be usedin two different circuits or can be connected together for obtaining alarger Variable capacitor.

The center of this rotor has a metal bushing 99 which is groundedthrough the shaft |05 of the motor |06 (Fig. 9) rotating it, and alsotwo small metal sectors |9911, |001), connecting each of the blades 96aand 96h. A brush ||l| is riding alternately either over the dielectricor over the grounded metal sectors in such a way as to pass from metalto dielectric exactly at the moment of maximum or minimum capacity ofthe condenser. This brush periodically discharges condenser |il2 to theground which condenser becomes charged through a resistor |03 when thebrush rides over the dielectric.

Just as in Fig. 4a, the condenser |92 becomes a mechanical source ofsweep voltage which is noiseless because the only frictional contactwhich takes place is to either the dielectric or to a grounded part ofthe receiver, which is not a part of the tuned circuit.

The electrical connections of such a synchronized dielectric condenserand sweep voltage generator are shown in Fig. 9 in which, for the sakeof simplicity, I show only one periodically tuned circuit, an oscillatorwhich can be the element B of the block diagrams. The synchronizedcondenser and sweep generator replace the elements F and G of thosediagrams.

By a slight addition to this construction, I can obtain an alternatingcoverage of two bands shown on two dilferent lines on the screen of thecathode ray tube, as shown in block diagram, Fig. 5.

On the same shaft |05 of this rotor, I mount a commutator composed oftwo equal sectors |01 and |98, Fig. 10, of double the opening of theblades a, SSb, that is 180. One of these sectors is of metal andgrounded to the shaft, and thence to the chassis; the other sector is ofan insulating material. A brush |09 is connected to a high resistancepotentiometer |G| connected on one side to a source of direct current(anode supply for example), and grounded on the other side. This brushwill be alternately at a certain voltage or at ground potential, as thecommutator rotates; a square-wave is -mechanicaly produced, and canserve through condenser ||2 for shifting the frequency sweep axis on thecathode ray tube as explained before. The same conimutator can serve foralternatingly selecting one of two condensers which tune the oscillatorcircuit, as illustrated in Fig. 11; it can also serve for mechanicallyshuttingoff or reducing the power of an altitude-indicating oscillator,as illustrated in Fig. 4a. Such a mechanical commutator can be' made toopen the cathode circuit of the oscillator t for predetermined periodsof time corresponding to the angle of the commutator sectors. Thetransmitter can be keyed ori, for example, alternately during each partof that rotation cycle which produces image of signals on the screen ofthe receiver.

Mechanical means for producing two band frequency scanning panoramicreception can be better seen in Fig. l1 where, instead of having thecondenser II permanently connected in the tuning circuit, I show twocondensers I I and I I3, each being alternately connected throughbrushes shown respectively at IIe and m3, to the ground.

The diierent frequency portions are, therefore, alternately covered bythe rotating condenser 96-9? previously described. By individuallytuning the condensers II and H3, each band may be separately tuned.Condenser II can, as shown in Figs. e and 1l, be controlled by apressure controlled device as an aneroid cell whereas the condenser I i3can be manually controlled for special purposes, as shown hereinafter(Fig. 21).

The block diagram of Fig. 5 can be fully adapted to this arrangement.

The type of mechanical sweep by means of,

rotating commutators described has one disadvantage; one part of theimages are lost by grounding the condenser |02 part of the time. Theresult of this is more tendency to flicker 'and less brilliancy of theimage as can be seen from Fig. 12. I can, however, advantageouslycombine electronic tuning and mechanically produced periodical voltagewith eliminationA of this disadvantage, as shown in Figs. 4a and 13.

In Fig, 13 the condenser I0?. has been replaced by a sawtooth oscillatorI6 Whose grid 89 is synchronized to a mechanical square-wave generatorsimilar to the one heretofore described, but using the 90 sectors, Iila,0311, Ib, i031).

This form of sector alternately switches in the tuning circuitcondensers i I and H3, at double the rate obtained before. The number ofimages obtained on the screen is double, because each alternate sawtoothcycle serves to put on the screen one of the frequency bands covered.

Special condensers giving variations of capacity from minimum to maximumover a greater portion of a rotating cycle, however (270 or more), canbe used advantageously to reduce the loss of images mentioned above.

In Fig. 1, I have shown a simple transmitteroscillator whose frequencyis controlled by the local atmospheric pressure. I can supplement thisinformation with that of a direction, which may be readily interpretedto indicate a given course, or to directly indicate right and left withrespect to said course. Two transmitting antenna have to be used eachoperating on a frequency slightly diierent from the other, and emittinga directional signal in such an angular relation to each other, as tocreate an equi-signal path along said course. This method, however, ismore completely described in my U. S. Patent No. 2,312,203, grantedFebruary 23, 1943.

Fig. 141 shows such an arrangement in which T1 and T2 are suchtransmitters, each feeding respectively into the dipoles A1 and A2 atright angles, whereby the courses X1, X2 and Y1, Y2 are created.supposing now that a 3.5 mc` bandwidth (for example, from 122.5 to 125mc.) is spread over 2.5 inches of a cathode ray tube screen; thisrepresents a frequency spacing of 1 megacycle per inch, and a one-eighthinch separation between Vtwo signals represents 0.125 mc. If the twosignals produced by T1 and T2 are, in other words, 0.125 mc. apart fromeach other, they will appear on the screen as two deflections separatedby M3". If an observer is on the equisignal path, the peaks of the twodenections will appear equally high. If he is on one side, or the other,one peak, or the other', will predominate. The linear difference betweenthe deections, corresponding to the amplitude ratio of the ,two signals,will indicate the number of degrees offcourse.

I have found that it is essential to keep the difference of wave-lengthsbetween these signals as small as possible, so that the number ofwavelengths traveled oy each signal within a few miles from thestation-where the signals are generally more erratic and more subjectedto the effects of reflection from obstacles-should be substantiallyequal, or differing only by a few wave-lengths. This reduces to aminimum the number of points where false indications could be obtainedif this difference would be greater. This is a fundamental part of myinvention distinguishing it from the usual type of dual frequency radioranges, where no special precautions are taken to maintain thiswavelength` separation within a minimum value. The frequency scanningpanoramic receiver can be made of sufficient selectivity to distinguishbetween two carriers of any frequency separation, as there are nointerfering side-bands such as would be produced by modulating suchcarriersl Two signals of very close frequency with their antennaelements quite close to each other are difficult, however, to maintainproperly tuned. There is a tendency for these two signals to pull eachother in synchronism or to create side-bands by becoming intermodulated.

By proper shielding precautions, it is possible to run the twotransmitters together as shown in Fig.' 14.

I can avoid, however, completely these difficulties, by sending signalsintermittently through each antenna, in such a manner that when one ison. the other is off. This is represented in Fig. 19, in which T1 and T2represent the two transmitting circuits including their radiators,emitting signals on adjacent frequencies, and O' represents a sourcewhich causes theseradiators to operate alternately. This switching ofthe radiators can be obtained either mechanicallyV or electronically.The first method has the advantage of great simplicity.

In all these transmitter arrangements, the frequency or frequencies, canbe either fixed or can vary within certain limits as controlled by lafrequency controlling elementY such as an aneroid barometer, as shown inFig. 1.

In the latter case, and provided that the aneroid cells used inthese'tr'ansmitters arecperating in identical condition, the groundtransmitting stations can be used to give absolute altitude indicationto the planes in their neighborhood, because both plane receivers andground transmitters are submitted to similar atmospheric conditions.

The two antennas, whose orientation determines certain courses, caneither be fixed or of variable orientation-and can be mounted either onaxed body, or on a mobile body. I

In order to extend the number of stations which can be used along Vagiven distance, and not to crowd them too much on the screen of acathode ray tube of relatively small diameter, I

prefer in .some .cases to `combine band extension and "some manualtuning with `frequency scanning panoramic tuning and, at the same time,use an indicator `showing what `part of the `band is tuned in. Thisindicator `can be calibrated in units of Adistance or of altitude, orany other convenient units. -Such an arrangement isshown in Fig. 21 inwhich the `screen |41 of :a .two-'band receiver is shown; |42 is aslider whichcanmove to right orfleft within certain limits by the actionof idler pulleys I 43, |44 and manually controlled pulley |45, overwhich a steel string 146 is wound. This string is connected tothe twoends of thezslider |42.

This slider can move so Vthat either end of .it can come in line withone extremity of Ythe screen ofthe cathode ray tube. It is calibrated.in miles, and their separation corresponds to the separation `betweensignals appearing on the cathode ray tube screen; for example, as shownin Fig. `21, when all the way to the right it will lshow the stationsfrom the reference point (zero miles) up to 200miles and when all theway to the lett it will show the stations from 200 miles up to 400miles. This is obtained by connecting the same pulley 145 with the shafti4? of a rotorof a condenser ||3 (see Figs. 11 and 13). rA .frame inthis slider permits insertion of a card showing in their spatialrelationship a series of beacon stations, for example from Chicago toErie. Each beacon station may determine either `a twocourse or afour-course route, according tothe type of antennas they use. A flierstarting from Chicago will set condenser H3 fully in, for lowestfrequency (Fmin) and the slider will, by this motion, move to itsextreme right position, and the beginning of the dial on the leftcorresponding to distance zero, indicating Chicago, will correspond toFmin on the screen. The dual 'frequency beacons will appear one afterthe other, further to the right, as the ier progresses along the course,several being seen accordingr to Vtheir signal strengths. The observercan, if he wishes to, gradually bring them to the center andcontinuously maintain the true relationship between the reading on thecard |48, mileage indication on slider |42 and position of the signalAon screen |4l. Such band spreading arrangement as shown is theequivalent of multiplying the diameter of the screen by two. Naturallythis can be multiplied still more if desired. As the flier reaches theend ofthe course marked on the card, he enters a new zone where the'frequencies Fmin-Fmsx are repeated and he repaces the card |48 with anew one, resetting his dial to zero miles. By reducing to Zero the sweepvoltage applied through potentiometer 2S tothe reactance tube, such areceiver becomes an ordinary uni-signal receiver tuned at the centerfrequency defined hereinabove. A switch 285 which has this function isshown in Fig. 4o. The device 34a, Fig. 4a, will then reproduce theauditive signal of any station which corresponds to that centerfrequency and which can be marked as a hairline on the center of theoscillograph screen (Fig. 21).

This dial arrangement can very well be used with either a single-band ora two-band frequency scanning panoramic receiver, such 'as shown inFigs. 5, 6, 7, 11 and 13,\in which iatter case, :one band is controlledby `a manual setting suchas just described (condenser |13), :and theother band by an automatic setting (condenser `I l) determined, forexample, :.by fan `aneroid cell, `and wherein one :setting `does `notdisturb fthe pther 18 one due to the independence of their tuningelements.

Fig. :21 shows such a combination: `above the screen `i4| :an Aaltitudescale |48' is used with'the top frequency axis showing O 'in its center.It is calibrated in altitudes up to 2000 feet above to the right, and20.00 feet lbelow to the left of the center line. An independent,ordinary altimeter dial |49 maybe set nearby, to give the actualaltitude which in Fig. 21 is 5200 feet.

A signal 4|50 .appears on the screen, above vthe line-of Abeaconsignals, indicating the presence of a warning station about 1000 feetabove the observer, in :other words, at 6200 feet. This may be a`mountain peak oranother plane, and this matter is easily determined, asit will be explained hereinafter, according to the rate of blinking of.interruption ofthe signal.

Tn Athe first case, the pilot knows that he must rise until the signalpasses to the left of the-center line, that is, below him.

AIn the second case, certain traic regulations are applied and as eachpilot either goes higher or lower, their respective change of positionis seen by the two observers in their receivers. Where a receiver suchas shown in Fig. 1l isused, the lateral `position of the deflections onthe lower frequencyaxis remain independent oi the change in the lateralposition of the deiiections on the upper .frequency axis because the twofrequency bands to which they correspond are independently controlledfor the upper and lower line. With reference to Fig. 1l for example,-the upper line deflections are controlled by the condenser (which inits turn is controlld by an aneroid cell), and `the lower linedeflections by condenser ||3 which .may be manually controlled. The twofunctions, however, may be separated if desired and two screensbe used,one only for airway beacons andanother forstratoscope indications.

Fig. 15 shows a single-band stratoscope screen inwhich the frequencyaxis is produced vertically. Three different calibrations appear to theright; the rstissof feet above and below, the second is '1500 feet aboveand below and the third is 4500 feet above and below. A three-positionknob 2Gb is shown below, :permitting the selection of any desired bandspread. This control is shown on Fig. 4u, as an arm moving over themultitapped resistor 20a. A dual-frequency directional beacon is shown500 Yreet below and three obstacles ,at various altitudes above theobserver. The amplitude axis is calibrated in miles corresponding to thestrength of stations of equal, standardized power.

Fig. 16 shows 'the screen-of a receiver calibrated in heights from 0 to10,000 feet, to be used by the traflic controlling authorities. It isnecessary to either tune this receiver oradjust its altitude scale up ordown according to local atmospheric pressure. This tuning or adjustmentcan be made either manually, or automatically, by means lof ana-neroidcell such as explained above. An inclined `line marked glide pathindicates the amplitudes expected from aircraft engaged along theglidepath'and their respective distances `can be ,rea-d on the lower scale.

Airway :trafic control- It is possible ltoinsta'll panoramic receiversfor airport train-c control'but minus the `catllode ray tube, `atvarious points along airways, and to convey the electric-impulses'crea-tingthe deflections oi'thecathode ray, toa distant ypointsituated at a traiiio control lcenter.

These I impulses are-of two kinds; aperiodic `voltage which produces thecathode ray sweep and the short impulses created by the sig-halsthemselves. There is no need to convey the rst type of impulses, becausethese can be exactly reproduced at the traffic control center. If, forexample, a source of 60 cycles alternating current is available, both atthe point where the receiver is installed along the airway, and at thecontrol center, an identical sawtooth voltage or any other type of wavehaving a predetermined shape, can be produced in both places, in perfectsynchronism by known methods. It is possible, however, to use directlythe sinusoidal current for the panoramic reception, as it will be shownseparately, and in this case the solution is still simpler, because wedispose at both places of the required sweep voltage. The signalimpulses can be sent either by wire or by radio communication accordingto well known methods which do not require description.

The use of sinusoidal currents for sweeping the cathode ray, incombination with another type of wave for the frequency sweep of theoscillator, results in an advantageous spacing of the signals on thescreen, which spreads the frequency scale toward the center andcompresses it toward the extremities. This is a desirable thing in astratoscope because it is important to be able to read more accuratelyvariations of vertical levels produced nearer the level of the aircraft,rather than at much higher or lower levels. In Fig. 15, I show such aspacing. Furthermore, the use of sine wave simplies certain constructionproblems such as, the generation of a Special sweep voltage and thediiculties of sending such types of current undistorted over long lines,for example, from one end to the other of a fuselage. Such sine wavescan be used advantageously also for keying or modulating the stratoscopetransmitter.

The simplest use of sine wave is to apply it simultaneously to the grid43 of the reactance tube I and to the cathode ray deecting element 63,Figs. #i and ea. This eliminates also the need of an amplifier tube suchas Il, as I can obtain the sufficient A. C. voltage directly from atransformer. In order to obtain, however, the desirable non-linearfrequency spacing shown in Fig. 15, I must use a wave 0f pyramid formfor the frequency sweep. The simplest way to do this is by using arotating 180 condenser plate to create the necessary periodical tuning(S6-91, Fig. 11). Such .a condenser actually produces a pyramidvariation of capacity (or frequency) versus rotation (or time), as shownin Fig. 12.

A motor generator such as 106 producing some A. C. Voltage, can be usedfor supplying both the sine wave required and the motive force for sucha condenser variation. Fig. 17 showsthe relationship between the variouselements. Curve S shows Vthe sine wave producing the cathode ray sweepvoltage varying between `+E and -E. Curve C shows the variations offrequency or of the frequency scanning panoramic receiver, between Fmand FM passing through a center frequency Fc. These two are in phase toeach other, passing through their extreme values at the same time. Asthe elements ab and bc on curve S are equal but opposite in direction,and as elements ab and bc on curve C are also equal and opposite indirection, the spot on the screen will travel over the same line backand'forth, faster in the center and slower nearer the ends o f thefrequency axis. On this Fig. 17, the curve M shows how the stratoscopetransmitter may be modulated with the same sine wave so to obtainl the20 periodical interruption, or modulation, required at the centerfrequency. This line represents a rectified sine wave of the samefrequency as S, as shown by the dotted lines showing the original,non-rectified current. By supplying such a rectified current to theplate supply of tube 6 (Fig. 4) marked +B, I obtain directly the exactmodulation required for rendering the transmitter either completelyinoperative, or operative at its lowest plate current, when thefrequency scanning panoramic receiver tunes through Fc, the transmittersfrequency. This is illustrated in Fig. 1'7 by the vertical groups ofparallel lines passing close to points d, e, f, g, h on curve C.Thesenlines meet the transmitter plate current curve M along adottedline showing the low current limit where the transmitter stopsoscillating. The same results can also be obtained by supplying D. C.plate voltage to-l-B and using the sine wave for grid modulation, forexample, the grid 68 at tube 22. Also, instead of using rectied sinewave, the same results can be obtained by using a sine wave of doublefrequency of S in the proper phase relationship. The phase shift betweensweep frequency and modulating frequency can be obtained by a simplecondenser resistance network, and if this is necessary it is preferablyused for the sweep voltage, where there is no power required. Thecondenser plate can, naturally, be mounted so as to remain in phase withthat sweep voltage at all times. The capacity variations required forperiodically tuning the oscillator, need not take place at or near theoscillator. By using large value capacity, the oscillator coil H5 (Fig.11) can be tapped down and the lead can be brought to a certaindistance.

Station identification-The identification of stations may be obtained invarious manners with a panoramic receiver, and in ways impossible to beobtained with ordinary receivers.

One of the means which can be used is the rate of interruption of asignal. From the foregoing explanations, it results that either thedualfrequency beacons, or the collision warning signals Sent by planesare periodically interrupted or modulated signals. This rate ofinterruption or modulation can be determined easily, provided that thefrequency sweep rate of the frequency scanning panoramic receiver isadjustable. This can be obtained very readily with the electronicallycontrolled sweeps shownand I have provided the necessary controls forthis purpose (seeV 84--31, Fig. 4). In a mechanically controlledreceiver, continuously adjustable speed devices can be used for thispurpose, either by varying the speed of the motor itself or of thedevices connecting the motor to the receiver.

High frequency sweeps are advantageous when many identifying frequenciesare required. In order to be able to use very high frequency sweeps ofthe order of a few hundred to a few thousand cycles per second, Ipreferapplying directly to the plate B2 of the cathode ray tube,non-rectified intermediate frequency signals obtained from transformeril (Fig. Il). Inthis case, the deflections appear on both sides of thefrequency sweep axis and take a distinctive appearance which in thestratoscope is very ap-k propriate; they look like the'wings of an air-`plane, seen from the front.

Y By synchronizing the sweep frequency with the frequency of modulationof a signal, I can receive that signal as if it was of unchanging naturebecause every time the receiver sweeps through .the frequency ofthe'signal, the signal is picked up at the same amplitude. If such asignal is `interrupted periodically, a perfect synchronism could causeit to be absent in the panoramic receiver entirely. This can happen inca'se of collision signals sent by planes, which could -be synchronizedby chance with a receiver, so Vthat they would not be received. This,however, would require a combination of coincidental factors, rarely metin practice; Ythe two receivers in two different planes would have to beswept in Vabsolute synchronism and be tuned to the s-ame frequencycontinuously. The chance of this condition occurring is remote and isfurther reduced by reducing the total interruption time of the collisionwarning transmitter to the shortest possible limit.

"-Ihe dual-frequency beacons forming part of a common system can bealternatelykeyed on and off at one and the same frequency rate deter-`ini-ned by properly adjusting the keying freqnency of element -O inFig. 19. The observer can `also adjust the sweep frequency of hisreceiver so as to see, for example, a very slow Vchange -of onefrequency to another, or he may stop (momentarily and during theidentication test) "the signal on one frequency only.

"-By noting the `position of the sweep frequency controls at which thisoccurs, the pilot can distinguish one :set of signals from another set.One set of beacons lmay have for example, an on-off rate of '27 cyclesper second, another one of 32 cycles per second, and vthe differentsettings he would `require on his receiver to freeze one set of motionswill tell him which set he is considering. This synchronizing is alsouseful for eliminating -certain forms of recurrent noises, such as frommotors or vibrators. The sweep frequency of -the receiver can beadjusted in synchronism with-the source of noise, whereby such noisesig- 'nals become frozen in a xed part of the screen where they cause nointerference, or may be entirelyeliminated.

Dual frequency beacons, therefore, can be made -to give characteristicsignals which generally appear as two adjacent V-like deflections,closing at the bottom. They cannot be mistaken for `ordinary unmodulatedsignals which are open at the bottom. Such beacons can be, if desired,code or voice modulated at certain Xed intervals. The pilot, having astratoscope on board with a selective auditive device, such as shown inFig.-4a (35a, c, d), can read such code and identify -the station. Phonecan be heard on a strat- 4oscope receiver by simply switching oft thefrequency sweep and transmitter (switches 205, fW36), and turning on theswitch 28 which cuts olf the phone chopper. In this case the receiverremains tuned to its center frequency, but it is possible to provide ameans to retune temporarily the receiver separately and independentlyVfrom the cell Ib, by bias tuning, that is byV varying the bias voltageapplied to the grid of the reactance tube l5, through the potenti-Aome'ter 19. In thiscase, I obtain the equivalent vof an ordinary radioreceiver, tunable over a frequency range and permitting two-waycommunication Ywith another station. The stratoscope transmitter 6, Fig.4a, can then be voicemoduated in the usual manner, for example, by theuse Vof a microphone in its cathode circuit its-witch 295) Itewill stillbe tuned by the aneroid cell and, therefore, continue to emit collisionwarnings :visible on the screens of other receivers.

Aircraft also can be identified, either by the ground observers, or bypilots Vof other aircraft,

vaccording toa characteristic -ra'te of modulation which vis assigned toeach. Such a'modulation iis produced by the periodic transmittermodulator 260e, 2ld, shown in Fig. 4a. By assigning various modulationfrequencies the probabilities of two aircraft operating in absolutevsynchronism are greatly reduced. By making the motor 105 rotate at aspeed proportional `to the air fspeed of an aircraft, the modulationrate can .be used as an indication of speed. Planes dying `in formationcan maintain constant .speed Vby maintaining their indications insynchronism.

Further identification can be added by imodulating the emitted signalswith code or even'voice, by'simply providing each transmitter with `acode wheel or a 'modulator and a voice record. The

chopper AZilc---Zild itself can lbe made to have as many .inserts 200eas desired, andthe inserts can be of any desired angular size formodulating the transmitter 6 according to CW or as :a 'given tone. Apickup can be put in its cathode Jcircu-it which is shown open by switch255.

'Two-course beacons are to bepreferred to .fourcourse beacons, becausethey can be made to agi-ve a positive indication of right and left InFig. 22 I show a course Xi-Xz vdetermined by such a dual-frequencybeacon located at O and alternately emitting on each side of the coursesignals L and R on adjacent frequencies Fr. and FR. Suppose thatfrequency 1FL is higher than that of Fn, and a plane carrying .apanoramic receiver ies in the Adirection of the arrow 'from `X1 to X2.If the screen of this receiver is so disposed that higher frequenciesare to the left, and if the plane happens -to be 4on the left side ofthe line iXi-X2, for example, in points Y1 or Y2, the left hand 'signalbecomes taller 'than the right'hand signal (see F-ig. 22a) andviceversa, if it happens 'tobe on the right 'side Ys or Yi, the righthand signal becomes taller ythan `the left hand signal (see Fig. 22h)Beacons giving, in combination, a number of simultaneous indicationsAcan thus be made. As an `example, I shall describe one whichsimultaneously indicates: altitudeof la point, barometric correction,wind direction and velocity. This is simply a combination of theprinciples described above. The beacon kis a dual-frequency two-courseradio range transmitter, whose average frequency is determined by abarometer controlled oscillator as explained from which'he can determinehis height above vthe ground.

The antennas of those two "transmitters determine a course similar toX1-X2 of Fig. 22, but this course is orientable according to winddirection, by pivoting .the antenna array around acentral point. Fig. 23shows in simplified form an upper view of such an 'antenna array inwhich ISI, |62 are the vertical antennas. each connected to onetransmitter. Each antenna-acts as a reector for the other when oneworks, obtaining as a result, two patterns opposed in phase, showndiagrammatically as 53 and I 54.

It is clear that the use of Ya stratoscope on board an aircraft permitsadditional possibilities, somepf which I^will now describe. Airways Icanbefestablis'hed, which are definednot only by their direction, `buttheir height as well. If the average frequency of a Adual-frequencydirection indicating beacon ismade to correspond to a Vpredeterminedaltitude-frequency, a stratoscope will indicate the Apresence of suchabeacon only when the yaircraft willfly'within certain vertical levels.At a given altitude, the beacon deflect-ion will appear on the-reenter-line of thestratoscope screen,

If the aircraft is above or below that level, the deflection will appearbelow or above that line. It is, therefore, possible to regulate trafficalong such airways, and maintain a one-way tramo above thatpredetermined level up to a certain maximum limit and traffic in thecontrary direction below that level down to a minimum vertical level.For example, an airway running east- West can be marked by a series ofbeacons 25-50 miles apart, whose frequencies correspond to heights of7500 feet above ground. Pilots flying eastY will be directed to ily soas to see the airway beacon deflections appear between 250 and 1500 feetabove their level and those flying west will have to maintain altitudesshowing these beacon deilections appearing between 250 and 1500 feetbelow their level. There willalways be, therefore, a minimum verticalseparation of 500 feet between aircraft running in opposite directions,which will inherently increase the safety of air traveling.

These conditions are represented in Fig. 18, in which A, B, C representa series of ground stations, each emitting a signal corresponding to analtitude frequency of 7500 feet. rThis means that each of thesetransmitters is adjusted by means of a barometer condenser which variesa certain mean frequency according to weather conditions. This meanfrequency is set at the beginning to represent the local altitude ofpoints A, B, C, etc., plus '7500 feet, the height of the center level ofthe airway.

The flier will, therefore, follow more or less the general contour ofthe earth and will know at all times his actual altitude from theposition of the airway beacons. Where such an airway crosses anotherone, the latter can be either higher or lower in altitude. By using theband compression switch the signals from two airways can be seensimultaneously on the screen so that the flier can pick up the otherairway when required, knowing whether he must ascend or descend. Simpletraffic rules can be evolved whereby a pilot passing from one airwayinto another must make certain regulation turns, taking him down or upto the required level without danger of collision.

Such vertically separated airways have the additional advantage ofpermitting a better check uprof traic conditions along airways by thetraffic control centers. By installing receivers at airwayintersections, it will be easy to know the number of planes going ineach direction, according to their vertical levels.

Aircraft can be lead from one elevated airway to another one, which maybe higher` or lower, or to an airport by means of vertical level mark-Vers, whose frequency is adjusted to indicate a certain altitude above agiven point. Their pattern of transmission is fan-like. Fig. 20 shows asys-Y tem of markers gradually leading a plane from an airway at 7500feet altitude toa landing runway. The horizontal line shows a stretch of14 miles from the point where the plane must touch the wheels to theground and the curve following in landing. Points a, b, c, d, e, f,represent landing markers which emit frequencies co1'- responding to thealtitudes of, for example, 5000 feet, 3000 feet, 2000 feet, 15'00 feet,1000 feet, 500 feet.Y They can be dual-frequency directional .beaconslined upto lead the aircraft along either a straight or curved path. Thepilot coming along an airway, for example, at 6500 feet altitude, willsee the signal from the marker a at 1.500 Yfeet below him and will takea steep glide to bring that marker in the center line (at which momenthe may also hear it in the phones). vI-Ie will continue that steepdescent and will then see the marker b, which may indicate a slightchange of direction. By passing its maximum signal through the -centerof the screen he will know that he is at the proper distance (in ourcase 10 miles) and proper altitude (3000 feet) for that distance. Thesame procedure will be followed for marker c which brings him to 2000feet, at eight miles, then to marker d, which brings him to 1500 feet,at six miles. At that moment he sees appearing on the lower edge of thescreen the airport altitude and runway beacon; this is also adual-frequency beacon, barometrically controlled, which indicates theairport altitude by its frequency and the direction of the runway by thetwo peaks it produces.

For the moment he sees this beacon until he reaches marker e (1000feet,.four miles), the pilot must enter in the normal glide path of theplane which will lead him to a landing. This glide path can be followedby maintaining a predetermined relationship between deection amplitudeand altitude. In Fig. 15 line A represents the variation of a signalwhich increases in strength as the point O on the runway is approached.The line B represents an equi-potential glide path obtainable byproperly shaping the transmission pattern of the airport altitude andrunway beacon. Either type of line can be used. The last -200 feet ofaltitude can be read with greater precision by panoramic bandspread. Anoutline of an aircraft appears on the center of the screen to betterconvey to the pilot a sense of his vertical position with respect to theobstacles represented thereon.

Beacons such as just described may be used in an emergency landingfield, where a pilot can make a landing even if no personnel is there toassist him. His stratoscope will indicate if the field is clear and noother planes are there, or if there are, would indicate which plane islower and which would have the priority to make a landing.

Although I have mentioned aneroid cells as the controlling devices inthe system of my invention, I desire that it be understood that otherinstruments may be used to serve similarly and to impart a certainknowledge; for example, a tachometer or speedometer may be employed toindicate speed or velocity, a thermometer to indicate temperature, agyroscope to indicate direction, etc. Therefore, Vin some of my claims Ihave used the expression an independent controlling device to signifyany such device, which operates independently of the radio receiving ortransmitting system, but which controls the operation thereof.

Inthe methods I described, I have shown only specific examples forobtaining certain results, but, it will be understood that I can obtainsimilar results Yby many other combinations of the elements describedfor shifting frequencies, keying on and off oscillators, periodicallyselecting one between a plurality of circuits, etc.

In these specifications and in the claims which follow, the term'Yaneroidcell has been used to signify any device which is operated bychanges of altitude, whether through'changes of atmos.-

pheric pressure or of capacity to ground, etc. Its use in thestratoscope is to cause certain electrical or mechanical variationswhich change the tuning of a receiver or a transmitter.`

l While Ihave described my invention in cer-

